In general, the invention relates to the installation of a land grid array module to a printed wiring board.
Area array socket connectors are an evolving technology in which an electrical interconnection between mating surfaces is provided through a conductive interposer. One significant application of this technology is the socketing of land grid array modules directly to a printed wiring board, in which the electrical connection is achieved by aligning the contact array of the two mating surfaces and the interposer, then mechanically compressing the interposer. Land grid array sockets assemblies are prevalent today in the electronics industry to attach single-chip-modules to printed wiring boards.
One method of generating the force required to compress the interposer is to deflect a springplate connected to the module. One example of a land grid array socket assembly using this technique is shown in FIG. 1. In this example, a flat rigid backside stiffener 152 with attached load posts 138 is attached to a printed wiring board 144. A module 134 with attached land grid array interposer 136 and heatsink 130 is slid over the load posts 138. The load transfer sleeves 128 are slid over the load posts 138 and contact the heatsink 130. A load transfer plate 122 is placed over the load posts 138 and rests on the load transfer sleeves 128. A springplate 116 is then attached to the top end of the load post 138. An actuation screw 112 inserted in the springplate 116 is then tightened until a slight compressive force is exerted on the load transfer sleeves 128. The actuation screw 112 is then rotated a predetermined number of turns displacing the springplate 116 from the load transfer plate 122. The springplate 116 deflects as it is displaced, resulting in a tensile force being applied to the load posts 138. The load plate 122 distributes the compressive load in the screw 112 to the load transfer sleeves 128. The compressive force in the sleeves 128 forces the heatsink 130 and module 134 towards the printed wiring board 144 compressing the interposer 136 establishing electrical connection between the module 134 and printed wiring board 144.
One problem with this type of connection system is that determining when a slight compressive force is exerted on the load transfer sleeves is very subjective. If the installer does not accurately determine when a slight compressive force is exerted in the load sleeves, the displacement of the load plate from the springplate will be inaccurate causing an incorrect actuation force to be applied. If excessive actuation force is applied, components in the assembly may be damaged. If to little actuation force is applied, a good electrical connection between the module and printed wiring board may not be established.
The surface of the land grid array module that contacts the interposer has a plurality of electrical contact points that align with contact points on the printed wiring board. Each of the contact points on the module must compress the interposer in order to make electrical connection with the contacts on the printed wiring board. If the contact points do not compress the interposer equally, some electrical connections between the contacts on the module and printed wiring board will be better than others. Unequal electrical connections may cause the electrical circuits within the module to operate improperly. One reason for unequal compression of the interposer may be that the load sleeves are not of equal length. If the load sleeves are not of equal length, the longer sleeves will transmit more of the load from the load plate. Load sleeves with a higher load will compress the interposer more than load sleeves with a lesser load. Another cause for unequal compression of the interposer is that the actuation force is applied to the edges of the module. When the actuation force is applied and the interposer is compressed, the interposer imparts a reactive load on the module. Since the actuation force and the reactive force are exerted in different areas of the module, a torque on the module results. The torque on the module may cause the module to deflect away from the interposer. If the module deflects, the distance from the edge of the module to the board may be less than the distance from the center of the module to the board resulting in the interposer compressing more near the edge of the module.
What is therefore needed is a method and apparatus for installing land grid array modules that will provide a fixed and uniform actuation force to the module independent of component manufacturing tolerances and module deflection.
One aspect of the invention provides a method of actuating the electrical connection of a land grid array module to a printed wiring board. A topside actuation force is exerted between a load plate and a springplate. The actuation force is translated to a plurality of load columns operably connected to load posts, whereby electrically connecting the land grid array module to a printed wiring board. The load plate may comprise a springplate.
Another aspect of the invention provides a method of actuating the electrical connection of a land grid array module to a printed wiring board. A land grid array module is deflected and the printed wiring board is deflected complementary to the deflection of the module.
Another aspect of the invention provides an apparatus for actuating the electrical connection of a land grid array module to a printed wiring board utilizing a plurality of load posts, a first springplate operably connected to the load posts, a plurality of load columns, and a second springplate operably connected to the load columns. An actuation member is operably connected to the springplates, wherein a force resulting from the actuation member is distributed to the load columns to operably connect the land grid array module to the printed wiring board. The springplates comprise laminated material. The actuation member is a screw. A stop is included in the screw to limit the actuation force imparted on the springplate. The actuation member is centrally located on the spring plates. The load columns are slideably received onto load posts. A backside stiffener is operably attached to the load posts. The backside stiffener includes a local stiffener operably located on the backside stiffener.
Another aspect of the invention provides an apparatus for actuating the electrical connection of a land grid array module to a printed wiring board utilizing a plurality of load posts, a load plate operably connected to the load posts, a plurality of load columns, and a springplate operably connected to the load columns. An actuation screw is operably connected to the springplate, wherein a force resulting from the actuation screw is distributed to the load columns to operably connect the land grid array module to the printed wiring board. The springplate comprise laminated material. The load plate comprises a springplate. The screw includes a stop to limit the actuation force imparted on the springplate. The stop comprises a shoulder formed on the screw. The actuation screw is centrally located on the springplate. The load columns are slideably received onto load posts. A backside stiffener operably attached to the load posts. The backside stiffener includes a local stiffener operably located on the backside stiffener.
Another aspect of the invention provides an apparatus for actuating the electrical connection of a land grid array module to a printed wiring board utilizing an actuation assembly and a backside stiffener. The backside stiffener may include a local stiffener. The local stiffener causes a deflection in the printed wiring board complementary to the deflection of the module when the actuation force is applied. The local stiffener is positioned in a pocket included in the backside stiffener. The local stiffener contacts a pedestal formed in the pocket.